Polyacetal plastic gears are widely used in the industrial machine elements and often operated about lm/s pitch line velocity. But there is not enough experiment and research being done in this velocity area. Through the fatigue test of polyacetal gears, we provide the basic test results and estimate the equation of fatigue life from the fatigue life curves. For estimating the equation of fatigue life, we performs the test on two operating conditions. One is not limits the temperature of tooth flank, the other is preserving the temperature of tooth flank under specific limit. As the result, how the temperature of tooth flank affects the failure and the fatigue life of poly acetal gear are shown and the Unit-load and K-factor are determined which are need in the design of polyacetal plastic gear.